Multiple universe, or “multiverse,” theories, touted in recent books by physicists, remain as devoid of empirical support as when they were first proposed more than a half century ago. Illustration: Scientific American.

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Physics, more than any other field, lured me into science journalism. Although I majored in literature in college, I took courses in physics and astronomy and gobbled up books on the mysteries of quantum mechanics and cosmology.

For a lapsed Catholic like me, physics represented a kind of scientific theology, an empirical, rational way of probing the mysteries of existence. Physicists were discerning resonances between the smallest and largest scales of reality and spinning out astonishing conjectures about our universe and even other universes.

My favorite scientific theologian was John Wheeler. Musing over how observation seems to influence the outcome of quantum experiments, Wheeler challenged conventional objectivity and materialism, and hinted that we humans might not be just a cosmic afterthought. We live in a "participatory" cosmos, he proposed, which emerges from the interaction of consciousness and the physical realm.

Wheeler pointed out convergences between quantum mechanics and information theory. Invented in 1948 by Claude Shannon, information theory is a method for quantifying the improbability—the surprisingness, you might say—of a message. Wheeler conjectured that the "it" of objective, physical reality stems from "answers to yes-or-no questions, binary choices, bits." He summed up this notion in the koan-like phrase "it from bit."

Wheeler helped popularize the anthropic principle. Originally postulated by Brandon Carter, the principle purports to answer one of the deepest of all questions: Why are the laws of physics as we find them rather than some other way? What explains the precise strength of gravity and other constants of nature? The universe seems so, well, arbitrary. According to the anthropic principle, the universe must be as we observe it to be, because otherwise we wouldn't be here to observe it.

Moreover, our universe might be one of many. The big-bang theory led some physicists, including Einstein, to suggest that our cosmos will eventually stop expanding, collapse back in a "big crunch" and rebound in yet another big bang. According to the oscillating-universe hypothesis, this cycle of cosmic death and rebirth is never-ending. Friedrich Nietzsche tormented himself with a similar idea, which he called "eternal recurrence.” Everything we do, he feared, happens over and over again, ad infinitum.

Quantum mechanics--which implies that a fleck of light or matter, when we're not looking at it, dwells in a haze of probabilities--yielded an even weirder multiple-universe theory. In the late 1950s, Hugh Everett proposed that each particle wanders down every possible path—in other universes.

In the late 1980s, John Barrow and Frank Tipler proposed the omega-point hypothesis, a fusion of artificial intelligence and cosmology. In the not-so-distant future, Barrow and Tipler speculated, our machines will become superintelligent, autonomous beings, which will quickly embark from Earth and begin colonizing the galaxy. The machines will eventually transform the entire universe into a gigantic thinking machine.

When the universe stops expanding and collapses toward an infinitely small point, the density and computational power of this cosmic brain will spike toward infinity. This all-powerful, Godlike computer will be able to simulate any possible reality. I once asked Tipler if our reality could be a simulation created by pre-existing omega point. That's possible, he said, but not likely, given how much suffering there is in our world. Now that is scientific theology.

What can physicists do to top these far-out visions? Not much, if books written over the past decade by Sean Carroll, Michio Kaku, Max Tegmark, Leonard Susskind, Lisa Randall and other physicist/popularizers are any guide. For the most part, they merely recycle the once-startling propositions of Einstein, Carter, Everett, Wheeler, Barrow, Tipler--and Nietzsche and Borges, for that matter.

The old oscillating-universe theory is revived in Endless Universe by Paul Steinhardt and Neil Turok and in Cycles of Time by Roger Penrose. In The Beginning of Infinity, David Deutsch dusts off Everett’s many-worlds hypothesis. And in his co-written bestseller The Grand Design, Stephen Hawking touts a multiverse model based on string theory, which I once found fascinating but now view as “science fiction with equations.”

String theory postulates that reality consists of undetectable strings wriggling in undetectable extra dimensions, and it comes in an almost infinite number of versions. Trying to turn this bug into a feature, Hawking asserts that all the universes “predicted” by string theory actually exist; the anthropic principle explains why we find ourselves in this particular cosmos.

In his bestseller The Hidden Reality, Brian Greene extols all the many varieties of multiverse. Nietzsche's chilling vision of eternal recurrence, repackaged by Greene, becomes cute. In an infinite, eternal multiverse, Greene conjectures, everything must happen countless times. Somewhere out there your doppelgänger is reading this sentence, and elsewhere "she has skipped ahead or feels in need of a snack."

Greene’s suggestion that our universe may be a simulation run on the computer of an alien civilization is also old hat. These ideas, in fact, are just pseudo-scientific versions of stoner thought experiments: What if our whole world is just a grain of dirt in the pocket of a giant? And there is a whole universe inside one grain of dirt in our pockets? What if our world is really just an experiment created by evil machines? And so on.

Physicists' fantasies about parallel and virtual realms are not just stale. Increasingly, they strike me as escapist and even irresponsible, because they are so lacking in evidence. Scientists shouldn't have to serve the public good any more than poets or musicians. But if theories are being passed off as science, shouldn’t they have at least a remote chance of being empirically corroborated? Otherwise, how do they differ from pseudoscientific ideas like intelligent design?

Susan Sontag's 2002 essay "Looking at War" captures my jaded attitude toward speculation in physics, and especially the notion that our cosmos is virtual. Sontag castigated philosopher Jean Baudrillard, among others, for claiming that there is no reality anymore; there are only media "representations," "spectacles" and "simulated realities." This sort of philosophical claptrap, Sontag argued, is reprehensible in a world filled with real people suffering from real injustice, tyranny and wars.

To recapture its fizz, physics desperately needs not new ideas but new facts. Discoveries, not inventions. Ideally, physicists will stumble on something so startling that they abandon their pursuit of multiverses, strings and other fantasies and return to reality.

In the late 1990s, astronomers studying supernovas deduced to their astonishment that the expansion of the universe is speeding up. But this discovery, the most exciting since I became a science writer, has not forced radical revisions of the big-bang paradigm. Similarly, the Higgs boson, detected a few years ago by the Large Hadron Collider, merely confirmed the standard model of particle physics. Ho hum.

Things have gotten so bad that physicists are openly fretting about the future of their field. In a recent TED Talk, “Have we reached the end of physics?”, Harry Cliff states that “for the first time in the history of science, we could be facing questions that we cannot answer, not because we don't have the brains or technology, but because the laws of physics themselves forbid it.”

I still keep an eye on physics, but I doubt it will ever thrill me as it once did. My go-to source for fizzy ideas now is research into the brain and mind. Science’s wildest frontier is inside our heads.

Self-Plagiarism Alert: This essay is adapted from one originally published in The Chronicle of Higher Education.

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